Reference is made herein to an “undercut” bead, referring to the shape of the bead base (the radially inner surface of a tire bead that seats in the bead seat portion of a wheel rim). Tire bead bases are most commonly substantially flat and are angled from zero to several degrees relative to the axial direction with the bead base angle opening axially outward. An undercut bead base may be similarly shaped except that the bead base angle opens axially inward. Examples of tires with undercut bead bases, and examples of wheel rims using such tires, are seen in U.S. Pat. No. 6,092,575. In particular, it should be noted that a common variant of a tire with the undercut bead base design comprises beads of two different diameters on the same tire.
In order to mold certain tire constructions, such as those having undercut beads, it becomes necessary to introduce a portion of the tire mold known as the bead molding ring or counter-molding ring into the interior of the tire in order to engage a molding surface against the bead base. In the prior art, means are known for accomplishing the molding of an undercut portion of a tire bead. For example, U.S. Pat. No. 5,129,802 proposes using two counter-molding rings (bead molding rings) for the axially and radially inner portion of the bead, said rings being continuous. In order to introduce the counter-molding rings into the interior of the tire, it is necessary to deform the raw blank of the tire by ovalizing at least one of the beads, so that the bead can be made to pass beyond the counter-molding ring or rings.
Rings for molding the radially and axially inner portion of a bead have also been described in connection with so-called membrane-less vulcanizing presses. See, for example, U.S. Pat. No. 4,236,883 (referred to hereinafter as the '883 patent), which discloses such rings, in this instance made in several segments circumferentially adjacent in molding position. These rings are radially retractable so that they can be introduced into the tire interior without requiring deformation of the tire beads. The '883 patent describes a mechanism occupying integrally the inner volume of the press, so that the necessary movements can be imparted to the several ring segments in order for said segments to accommodate a closing or opening movement in sequence. By a “movement in sequence” is meant that, from a configuration in which the mold is open, the segments do not all go to their molding position at the same time. A first group is brought to its final molding position, then the segments of a second group are inserted between segments of the first group to make a continuous ring. As seen in the '883 patent's FIGS. 1-2, the first and second segments join along axially aligned planar surfaces, and all segments rotate into position by means of bellcranks (66) rotating on pivots (70) in depending clevis' (74). The bellcranks have cam followers that coact with a multi-faceted linear cam assembly (102) for controlled actuation of the segments mounted on the bellcranks.
U.S. Pat. No. 6,238,193 (referred to hereinafter as the '193 patent) discloses a mold for a tire and a vulcanizing press fitted to receive said mold: a mold for molding a tire having beads of different diameters, Φ0 being the minimum diameter of the tire area at the bead of smaller diameter, Φ2 being the minimum diameter of the tire area at the bead of greater diameter. The mold has two sidewall plates for molding, respectively, the outer surface of the sidewalls and the outer portion of each bead up to a radially inner limit where the diameter of the tire area is Φ0 and Φ2, respectively, a continuous counter-molding ring to mold the bead of smaller diameter from the said radially inner limit where the diameter of the tire area is Φ0 to an axially inner limit of diameter Φ1, where Φ1 is smaller than Φ2, and a split counter-molding ring to mold the bead of greater diameter from the said radially inner limit where the diameter of the tire area is Φ2 to an axially inner limit of diameter Φ3. As seen in the '193 patent's FIG. 1, the tire bead bases are undercut, i.e., Φ1 is greater than Φ0, and Φ3 is greater than Φ2. The split ring includes a plurality of retractable segments adjacent in molding position. A flexible membrane molds the inner surface of the tire in the portion of the inner cavity of the tire between the limit of diameter Φ1 and the limit of diameter Φ3.
As viewed in its FIGS. 2-11, the '193 patent discloses a complex mechanism for engaging the split counter-molding ring to mold the lower bead (the bead with the greater diameter). The split counter-molding ring is annular and comprises large segments (141) with beveled edges and smaller key segments (142) having corresponding beveled edges. The edges are beveled at an angle to the axial direction (see FIG. 4), so that the key segments can be fitted into the annular ring by moving axially down in between the large segments. After the segments have been fitted together (FIGS. 8-10), the ring is pressed down axially against the lower mold sidewall plate 12 to form the bead area (FIG. 11). A problem with the split counter-molding ring design is a complex set of linkages and mechanisms attached to the mold press that is difficult and expensive to manufacture, and that also makes maintaining and changing the vulcanizing mold in the press a time-consuming and difficult process. As viewed in the '193 patent's FIG. 2, the split counter-molding ring (14) comprises first segments (141) each mounted on a rocking arm (52), itself mounted rotatably on the slide (17) that is mounted on the lower frame 22 of the press. A roller (521) mounted on each of the rocking arms acts against a first cam 42 that is integral with the lower membrane plate (32). The second (key) segments (142) are mounted on a guide plate (321) in grooves (53) formed between said guide plate (321) and the first cam (42). A roller (531) is rotatably mounted on each of the second segments and rides against a second cam (43) fixed on the lower frame (22) of the press. The profile of the radially outer surface of said second cam (43) serves to impart a controlled motion for the advance of each of the second segments (142).
It is an object of the present invention to overcome the problems and limitations of the prior art tire molds, particularly molds using radially expandable bead molding rings, such as for molding undercut beads. Problems to be solved include reduction of mechanical complexity to simplify manufacturing of the molds, and to ease mold/press maintenance and changeover.